1. Field of the Invention
The present invention relates to a method of processing the measured thickness data signals produced in the course of the on-line measurement of the wall thickness of a pipe by the use of a rotary-type magnetic-ultrasonic wall thickness measuring apparatus.
2. Description of the Prior Art
Magnetic-ultrasonic wall thickness gages heretofore known in the art have been of the stationary type in which, as disclosed for example in Japanese Laid-Open Patent Nos. 57-203949, 57-203950 and 59-18452, a probe is fixedly placed in a given position relative to a material to be inspected and moreover it is so constructed that the magnetic flux produced from excitation coils arranged on the sides of the probe is passed in the longitudinal direction of the material to be inspected.
FIG. 13 of the accompanying drawings is a diagram for explaining a case in which the wall thickness of a steel pipe is measured by using conventional stationary magnetic-ultrasonic wall thickness gages. In Figure, numeral 100 designates a pipe to be inspected, and 200 stationary magnetic-ultrasonic wall-thickness gages which are arranged along the outer periphery of the pipe 100 at given intervals.
To measure the wall thickness, the pipe 100 is transferred at a given speed in the direction of an arrow a and in the excitation condition the probe (not shown) of each of the magnetic-ultrasonic wall thickness gages 200 transmits and receives a current pulse, thereby continuously measuring the wall thickness.
However, the conventional magnetic-ultrasonic wall thickness gage involves the following disadvantages.
(1) Since the magnetic flux passes in the longitudinal direction, there is the danger of magnetization in cases where the material to be inspected is a cold-worked steel pipe and the gage can be used only on hot-worked steel pipes. The reason is that in the case of a cold-worked steel pipe, there is the danger of the arc being caused to run out during the welding of the pipe ends thus giving risk to an inconvenience. Also, the provision of a demagnetizing operation is not suitable since it correspondingly complicates the process.
(2)Since the probe is complicated and large in construction and it can be used only in the stationary condition, the wall thickness cannot be measured along the whole periphery in the circumferential direction of a pipe. In the case of FIG. 13, each inspection track 201 is located on the longitudinal continuous straight line from the position at which the corresponding wall thickness gage 200 is arranged. As a result, it is impossible to measure the portion between the adjacent wall thickness gates 200, thus failing to provide a final quality assurance for the pipe.
(3) In order to measure the several circumferential locations of a pipe, several probes must be arranged in the circumferential direction of the pipe and the number of such probes is about 12 at the most. Also, in the case of a small-diameter pipe, it is impossible to arrange such a large number of probes. Thus, this is improper from the quality assurance point of view.
(4) Since the probes are constructed to be independent of one another, it is extremely expensive to arrange a large number of probes.
Then, as a means of overcoming these problems, there is known in the art a rotary-type magnetic-ultrasonic wall thickness measuring apparatus in which measuring heads are rotated about a pipe at a high speed. Its construction is shown in FIG. 11.
This rotary-type magnetic-ultrasonic wall thickness measuring apparatus 10 includes a rotary head 1 which is rotated at a high speed along the outer periphery of a pipe 100 to be inspected, and the rotary head 1 includes a ring yoke 2 having the common axis as the pipe 100, magnetic poles 3 and 4 which are arranged to project in a vertically opposite relationship on the inner side of the ring yoke 2 and two measuring heads 5 and 6 which are each supported on the rotary head 1 between the associated magnetic pole and the pipe 100 and having a plurality of longitudinal probes (not shown), thereby producing magnetic flux 7 passing in the circumferential direction of the pipe 100. In the Figure, numeral 8 designates magnetizing yokes, and 9 protective guides. The plurality of probes of each measuring head are arranged at given intervals in the longitudinal direction of the common magnetic pole.
While the operating principle of the rotary-type magnetic ultrasonic wall thickness measuring apparatus 10 is the same as the conventional gages, the pipe 100 is passed through the center of the rotary head 1 rotating at a speed of 1200 rpm at the maximum so that the resulting magnetic flux 7 is passed the circumferential direction of the pipe 100 thus eliminating the danger of magnetization and also the inspection tracks are in spiral form, thereby making it possible to measure the wall thickness of the pipe along its whole periphery in the circumferential direction irrespective of the pipe size.
The above-described rotary-type magnetic-ultrasonic wall thickness measuring apparatus has many advantages over the conventional gages of the stationary type and thus it is capable of performing an on-line inspection of the wall thickness of a steel pipe continuously along the whole periphery irrespective it being hot worked or cold worked and its pipe size.
Therefore, while the application of such rotary-type magnetic-ultrasonic wall thickness measuring apparatus to a continuous raw pipe in the pipe manufacturing process makes it possible to perform the desired high-speed and high-accuracy wall thickness measurement and discrimination, it is a general practice to supply products by cutting a single length of raw pipe into given lengths and therefore it is necessary to use a method for discriminating and processing large number of measured data groups individually for each of the products. In particular, where the wall thickness and inner diameter of the pipe ends are specified, a discriminating and processing method constitutes a particularly important problem and it is important from the standpoint of eliminating the off-line cutting and inspection, streamlining the inspection personnel and so on.